Ion implantation is a standard technique for introducing conductivity-altering impurities into a workpiece. A desired impurity material is ionized in an ion source, the ions are accelerated to form an ion beam of prescribed energy, and the ion beam is directed at the surface of the workpiece. The energetic ions in the beam penetrate into the bulk of the workpiece material and are embedded into the crystalline lattice of the workpiece material to form a region of desired conductivity.
Solar cells are one example of a device that uses silicon workpieces. Any reduced cost to the manufacture or production of high-performance solar cells or any efficiency improvement to high-performance solar cells would have a positive impact on the implementation of solar cells worldwide. This will enable the wider availability of this clean energy technology.
The doping pattern for certain types of solar cell, such as interdigitated back contact (IBC) solar cells, may include both p-type and n-type dopant regions disposed on the same surface of the solar cell. Certain portions of the surface may be implanted with p-type dopants to create emitters. Other portions are implanted with n-type dopants to create more negatively biased back surface fields. The surface may then be coated with a passivating layer to enhance the reflectivity. Metal fingers are attached to the emitter and to the BSF.
Thus, to form the IBC solar cell, two patterned doping processes may be performed. These patterned doping processes are aligned to prevent the p-type emitters and the n-type back surface fields from overlapping. Poor alignment or overlapping may be prevented by leaving a gap between the p-type emitter and the n-type back surface field, but this may degrade performance of the solar cell. Even when properly aligned, such patterned doping may have large manufacturing costs. For example, photolithography or hard masks (such as an oxide) may be used, but both are expensive and use extra fabrication processes.
Therefore, it would be beneficial if there were an improved method of high precision doping for solar cells and, more particularly, an improved method of high precision doping for IBC solar cells using ion implantation.